Load current control circuit

ABSTRACT

A system and method for operating one or more light emitting devices is disclosed. In one example, the intensity of light provided by the one or more light emitting devices is adjusted responsive to current feedback from the one or more light emitting devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional applicationSer. No. 13/830,887, entitled “LOAD CURRENT CONTROL CIRCUIT,” and filedon Mar. 14, 2013, which claims priority to U.S. Provisional PatentApplication No. 61/617,496, entitled “LOAD CURRENT CONTROL CIRCUIT,” andfiled on Mar. 29, 2012, the entire contents of each of which areincorporated herein by reference for all purposes.

BACKGROUND/SUMMARY

Solid-state lighting devices have many uses in industrial applications.Ultraviolet (UV) lighting devices have become fairly common for curingphoto sensitive media such as coatings, including inks, adhesives,preservatives, etc. Curing time of these photo sensitive media may becontrolled via adjusting intensity of light directed at the photosensitive media or the amount of time that the photo sensitive media isexposed to light from the solid-state lighting device. Solid-statelighting devices typically use less power, cost less and may have easierdisposal than current mercury arc lamp devices.

Solid-state lighting devices may consist of laser diodes orlight-emitting diodes (LEDs) as examples. The device typically has anarray or several arrays arranged to provide light with a particularprofile, such as a long, thin light region, or wider and deeper lightregions. The individual elements reside in arrays, a lighting device mayconsist of several arrays, or several arrays arranged in modules, withthe lighting device having several modules. If the solid state lightingdevices are supplied with a varying amount of current, or if differentgroups of photo sensitive media are exposed to light for differentdurations, photo sensitive curing times may vary or may be insufficientto provide a desired level of curing.

The inventor herein has recognized the above-mentioned disadvantages andhas developed a system for operating one or more light emitting devices,comprising: a voltage regulator including a feedback input, the voltageregulator in electrical communication with the one or more lightemitting devices; and a current sensing device positioned in a currentpath through which a current passes through the one or more lightemitting devices.

By controlling current flow through a lighting array based on currentfeedback, it may be possible to more precisely control light intensityof a lighting array. For example, current flowing through a variableresistance device may be controlled responsive to current flow that ismeasured flowing through a lighting array. As a result, current suppliedto the lighting array and light intensity may converge to desiredvalues. In other examples, a voltage output of a buck voltage regulatormay be adjusted responsive to current flowing through a lighting array.Current flowing through the lighting array is adjusted via varyingvoltage applied to the lighting array. In this way, the buck voltageregulator is adjusted responsive to current flow through the lightingarray so as to provide closed loop feedback control of current flowingthrough the lighting array.

The present description may provide several advantages. Specifically,the approach may improve lighting system light intensity control.Further, the approach may provide lower power consumption via providingefficient electrical current control. Further still, the approach may beprovided via alternative devices so that the design remains flexible andcost effective.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of a lighting system;

FIGS. 2-4 show schematics of example current regulating systems; and

FIG. 5 shows an example method for controlling current in aphotoreactive system.

DETAILED DESCRIPTION

The present description is related to a lighting system with regulatedcurrent. FIG. 1 shows one example lighting system in which regulatedcurrent control is provided. The lighting current control may beprovided according to example circuits as shown in FIGS. 2-4. However,alternative circuits that provide the described function or that operatesimilar to the circuits shown are also included within the scope of thedescription. The lighting system may be operated according to the methodof FIG. 5. Electrical interconnections shown between components in thevarious electrical diagrams represent current paths between theillustrate devices.

Referring now to FIG. 1, a block diagram of a photoreactive system 10 inaccordance with the system and method described herein is shown. In thisexample, the photoreactive system 10 comprises a lighting subsystem 100,a controller 108, a power source 102 and a cooling subsystem 18.

The lighting subsystem 100 may comprise a plurality of light emittingdevices 110. Light emitting devices 110 may be LED devices, for example.Selected of the plurality of light emitting devices 110 are implementedto provide radiant output 24. The radiant output 24 is directed to awork piece 26. Returned radiation 28 may be directed back to thelighting subsystem 100 from the work piece 26 (e.g., via reflection ofthe radiant output 24).

The radiant output 24 may be directed to the work piece 26 via couplingoptics 30. The coupling optics 30, if used, may be variouslyimplemented. As an example, the coupling optics may include one or morelayers, materials or other structure interposed between the lightemitting devices 110 providing radiant output 24 and the work piece 26.As an example, the coupling optics 30 may include a micro-lens array toenhance collection, condensing, collimation or otherwise the quality oreffective quantity of the radiant output 24. As another example, thecoupling optics 30 may include a micro-reflector array. In employingsuch micro-reflector array, each semiconductor device providing radiantoutput 24 may be disposed in a respective micro-reflector, on aone-to-one basis.

Each of the layers, materials or other structure may have a selectedindex of refraction. By properly selecting each index of refraction,reflection at interfaces between layers, materials and other structurein the path of the radiant output 24 (and/or returned radiation 28) maybe selectively controlled. As an example, by controlling differences insuch indexes of refraction at a selected interface disposed between thesemiconductor devices to the work piece 26, reflection at that interfacemay be reduced, eliminated, or minimized, so as to enhance thetransmission of radiant output at that interface for ultimate deliveryto the work piece 26.

The coupling optics 30 may be employed for various purposes. Examplepurposes include, among others, to protect the light emitting devices110, to retain cooling fluid associated with the cooling subsystem 18,to collect, condense and/or collimate the radiant output 24, to collect,direct or reject returned radiation 28, or for other purposes, alone orin combination. As a further example, the photoreactive system 10 mayemploy coupling optics 30 so as to enhance the effective quality orquantity of the radiant output 24, particularly as delivered to the workpiece 26.

Selected of the plurality of light emitting devices 110 may be coupledto the controller 108 via coupling electronics 22, so as to provide datato the controller 108. As described further below, the controller 108may also be implemented to control such data-providing semiconductordevices, e.g., via the coupling electronics 22.

The controller 108 preferably is also connected to, and is implementedto control, each of the power source 102 and the cooling subsystem 18.Moreover, the controller 108 may receive data from power source 102 andcooling subsystem 18.

The data received by the controller 108 from one or more of the powersource 102, the cooling subsystem 18, the lighting subsystem 100 may beof various types. As an example, the data may be representative of oneor more characteristics associated with coupled semiconductor devices110, respectively. As another example, the data may be representative ofone or more characteristics associated with the respective component 12,102, 18 providing the data. As still another example, the data may berepresentative of one or more characteristics associated with the workpiece 26 (e.g., representative of the radiant output energy or spectralcomponent(s) directed to the work piece). Moreover, the data may berepresentative of some combination of these characteristics.

The controller 108, in receipt of any such data, may be implemented torespond to that data. For example, responsive to such data from any suchcomponent, the controller 108 may be implemented to control one or moreof the power source 102, cooling subsystem 18, and lighting subsystem100 (including one or more such coupled semiconductor devices). As anexample, responsive to data from the lighting subsystem indicating thatthe light energy is insufficient at one or more points associated withthe work piece, the controller 108 may be implemented to either (a)increase the power source's supply of current and/or voltage to one ormore of the semiconductor devices 110, (b) increase cooling of thelighting subsystem via the cooling subsystem 18 (i.e., certain lightemitting devices, if cooled, provide greater radiant output), (c)increase the time during which the power is supplied to such devices, or(d) a combination of the above.

Individual semiconductor devices 110 (e.g., LED devices) of the lightingsubsystem 100 may be controlled independently by controller 108. Forexample, controller 108 may control a first group of one or moreindividual LED devices to emit light of a first intensity, wavelength,and the like, while controlling a second group of one or more individualLED devices to emit light of a different intensity, wavelength, and thelike. The first group of one or more individual LED devices may bewithin the same array of semiconductor devices 110, or may be from morethan one array of semiconductor devices 110. Arrays of semiconductordevices 110 may also be controlled independently by controller 108 fromother arrays of semiconductor devices 110 in lighting subsystem 100 bycontroller 108. For example, the semiconductor devices of a first arraymay be controlled to emit light of a first intensity, wavelength, andthe like, while those of a second array may be controlled to emit lightof a second intensity, wavelength, and the like.

As a further example, under a first set of conditions (e.g. for aspecific work piece, photoreaction, and/or set of operating conditions)controller 108 may operate photoreactive system 10 to implement a firstcontrol strategy, whereas under a second set of conditions (e.g. for aspecific work piece, photoreaction, and/or set of operating conditions)controller 108 may operate photoreactive system 10 to implement a secondcontrol strategy. As described above, the first control strategy mayinclude operating a first group of one or more individual semiconductordevices (e.g., LED devices) to emit light of a first intensity,wavelength, and the like, while the second control strategy may includeoperating a second group of one or more individual LED devices to emitlight of a second intensity, wavelength, and the like. The first groupof LED devices may be the same group of LED devices as the second group,and may span one or more arrays of LED devices, or may be a differentgroup of LED devices from the second group, and the different group ofLED devices may include a subset of one or more LED devices from thesecond group.

The cooling subsystem 18 is implemented to manage the thermal behaviorof the lighting subsystem 100. For example, generally, the coolingsubsystem 18 provides for cooling of such subsystem 12 and, morespecifically, the semiconductor devices 110. The cooling subsystem 18may also be implemented to cool the work piece 26 and/or the spacebetween the piece 26 and the photoreactive system 10 (e.g.,particularly, the lighting subsystem 100). For example, coolingsubsystem 18 may be an air or other fluid (e.g., water) cooling system.

The photoreactive system 10 may be used for various applications.Examples include, without limitation, curing applications ranging fromink printing to the fabrication of DVDs and lithography. Generally, theapplications in which the photoreactive system 10 is employed haveassociated parameters. That is, an application may include associatedoperating parameters as follows: provision of one or more levels ofradiant power, at one or more wavelengths, applied over one or moreperiods of time. In order to properly accomplish the photoreactionassociated with the application, optical power may need to be deliveredat or near the work piece at or above a one or more predetermined levelsof one or a plurality of these parameters (and/or for a certain time,times or range of times).

In order to follow an intended application's parameters, thesemiconductor devices 110 providing radiant output 24 may be operated inaccordance with various characteristics associated with theapplication's parameters, e.g., temperature, spectral distribution andradiant power. At the same time, the semiconductor devices 110 may havecertain operating specifications, which may be are associated with thesemiconductor devices' fabrication and, among other things, may befollowed in order to preclude destruction and/or forestall degradationof the devices. Other components of the photoreactive system 10 may alsohave associated operating specifications. These specifications mayinclude ranges (e.g., maximum and minimum) for operating temperaturesand applied, electrical power, among other parameter specifications.

Accordingly, the photoreactive system 10 supports monitoring of theapplication's parameters. In addition, the photoreactive system 10 mayprovide for monitoring of semiconductor devices 110, including theirrespective characteristics and specifications. Moreover, thephotoreactive system 10 may also provide for monitoring of selectedother components of the photoreactive system 10, including theirrespective characteristics and specifications.

Providing such monitoring may enable verification of the system's properoperation so that operation of photoreactive system 10 may be reliablyevaluated. For example, the system 10 may be operating in an undesirableway with respect to one or more of the application's parameters (e.g.,temperature, radiant power, etc.), any components characteristicsassociated with such parameters and/or any component's respectiveoperating specifications. The provision of monitoring may be responsiveand carried out in accordance with the data received by controller 108by one or more of the system's components.

Monitoring may also support control of the system's operation. Forexample, a control strategy may be implemented via the controller 108receiving and being responsive to data from one or more systemcomponents. This control, as described above, may be implementeddirectly (i.e., by controlling a component through control signalsdirected to the component, based on data respecting that componentsoperation) or indirectly (i.e., by controlling a component's operationthrough control signals directed to adjust operation of othercomponents). As an example, a semiconductor device's radiant output maybe adjusted indirectly through control signals directed to the powersource 102 that adjust power applied to the lighting subsystem 100and/or through control signals directed to the cooling subsystem 18 thatadjust cooling applied to the lighting subsystem 100.

Control strategies may be employed to enable and/or enhance the system'sproper operation and/or performance of the application. In a morespecific example, control may also be employed to enable and/or enhancebalance between the array's radiant output and its operatingtemperature, so as, e.g., to preclude heating the semiconductor devices110 or array of semiconductor devices 110 beyond their specificationswhile also directing radiant energy to the work piece 26 sufficient toproperly complete the photoreaction(s) of the application.

In some applications, high radiant power may be delivered to the workpiece 26. Accordingly, the subsystem 12 may be implemented using anarray of light emitting semiconductor devices 110. For example, thesubsystem 12 may be implemented using a high-density, light emittingdiode (LED) array. Although LED arrays may be used and are described indetail herein, it is understood that the semiconductor devices 110, andarray(s) of same, may be implemented using other light emittingtechnologies without departing from the principles of the description,examples of other light emitting technologies include, withoutlimitation, organic LEDs, laser diodes, other semiconductor lasers.

The plurality of semiconductor devices 110 may be provided in the formof an array 20, or an array of arrays. The array 20 may be implementedso that one or more, or most of the semiconductor devices 110 areconfigured to provide radiant output. At the same time, however, one ormore of the array's semiconductor devices 110 are implemented so as toprovide for monitoring selected of the array's characteristics. Themonitoring devices 36 may be selected from among the devices in thearray 20 and, for example, may have the same structure as the other,emitting devices. For example, the difference between emitting andmonitoring may be determined by the coupling electronics 22 associatedwith the particular semiconductor device (e.g., in a basic form, an LEDarray may have monitoring LEDs where the coupling electronics provides areverse current, and emitting LEDs where the coupling electronicsprovides a forward current).

Furthermore, based on coupling electronics, selected of thesemiconductor devices in the array 20 may be either/both multifunctiondevices and/or multimode devices, where (a) multifunction devices arecapable of detecting more than one characteristic (e.g., either radiantoutput, temperature, magnetic fields, vibration, pressure, acceleration,and other mechanical forces or deformations) and may be switched amongthese detection functions in accordance with the application parametersor other determinative factors and (b) multimode devices are capable ofemission, detection and some other mode (e.g., off) and are switchedamong modes in accordance with the application parameters or otherdeterminative factors.

Referring to FIG. 2, a schematic of a first lighting system circuit thatmay supply varying amounts of current is shown. Lighting system 100includes one or more light emitting devices 110. In this example, lightemitting devices 110 are light emitting diodes (LEDs). Each LED 110includes an anode 201 and a cathode 202. Switching power source 102shown in FIG. 1 supplies 48V DC power to voltage regulator 204 via pathor conductor 264. Voltage regulator 204 supplies DC power to the anodes201 of LEDs 110 via conductor or path 242. Voltage regulator 204 is alsoelectrically coupled to cathodes 202 of LEDs 110 via conductor or path240. Voltage regulator 204 is shown referenced to ground 260 and may bea buck regulator in one example. Controller 108 is shown in electricalcommunication with voltage regulator 204. In other examples, discreteinput generating devices (e.g., switches) may replace controller 108, ifdesired. Controller 108 includes central processing unit 290 forexecuting instructions. Controller 108 also includes inputs and outputs(I/O) 288 for operating voltage regulator 204 and other devices.Non-transitory executable instructions may be stored in read only memory292 while variables may be stored in random access memory 294. Voltageregulator 204 supplies an adjustable voltage to LEDs 110.

Variable resistor 220 in the form of a field-effect transistor (FET)receives an intensity signal voltage from controller 108 or via anotherinput device. While the present example describes the variable resistoras an FET, one must note that the circuit may employ other forms ofvariable resistors.

In this example, at least one element of array 20 includes solid-statelight-emitting elements such as light-emitting diodes (LEDs) or laserdiodes produce light. The elements may be configured as a single arrayon a substrate, multiple arrays on a substrate, several arrays eithersingle or multiple on several substrates connected together, etc. In oneexample, the array of light-emitting elements may consist of a SiliconLight Matrix™ (SLM) manufactured by Phoseon Technology, Inc.

The circuit shown in FIG. 2 is a closed loop current control circuit208. In closed loop circuit 208, the variable resistor 220 receives anintensity voltage control signal via conductor or path 230 through thedrive circuit 222. The variable resistor 220 receives its drive signalfrom the driver 222. Voltage between variable resistor 220 and array 20is controlled to a desired voltage as determined by voltage regulator204. The desired voltage value may be supplied by controller 108 oranother device, and voltage regulator 204 controls voltage signal 242 toa level that provides the desired voltage in a current path betweenarray 20 and variable resistor 220. Variable resistor 220 controlscurrent flow from array 20 to current sense resistor 255 in thedirection of arrow 245. The desired voltage may also be adjustedresponsive to the type of lighting device, type of work piece, curingparameters, and various other operating conditions. An electricalcurrent signal may be fed back along conductor or path 236 to controller108 or another device that adjusts the intensity voltage control signalprovided. In particular, if the electrical current signal is differentfrom a desired electrical current, the intensity voltage control signalpassed via conductor 230 is increased or decreased to adjust electricalcurrent through array 20. A feedback current signal indicative ofelectrical current flow through array 20 is directed via conductor 236as a voltage level that changes as electrical current flowing throughcurrent sense resistor 255 changes.

In one example where the voltage between variable resistor 220 and array20 is adjusted to a constant voltage, current flow through array 20 andvariable resistor 220 is adjusted via adjusting the resistance ofvariable resistor 220. Thus, a voltage signal carried along conductor240 from the variable resistor 220 does not go to the array 20 in thisexample. Instead, the voltage feedback between array 20 and variableresistor 220 follows conductor 240 and goes to a voltage regulator 204.The voltage regulator 204 then outputs a voltage signal 242 to the array20. Consequently, voltage regulator 204 adjusts its output voltage inresponse to a voltage downstream of array 20, and current flow througharray 20 is adjusted via variable resistor 220. Controller 108 mayinclude instructions to adjust a resistance value of variable resistor220 in response to array current fed back as a voltage via conductor236. Conductor 240 allows electrical communication between the cathodes202 of LEDs 110, input 299 (e.g., a drain of an N-channel MOSFET) ofvariable resistor 220, and voltage feedback input 293 of voltageregulator 204. Thus, the cathodes 202 of LEDs 110 an input side 299 ofvariable resistor 220 and voltage feedback input 299 are at the samevoltage potential.

The variable resistor may take the form of an FET, a bipolar transistor,a digital potentiometer or any electrically controllable, currentlimiting device. The drive circuit may take different forms dependingupon the variable resistor used. The closed loop system operates suchthat an output voltage regulator 204 remains about 0.5 V above a voltageto operate array 20. The regulator output voltage adjusts voltageapplied to array 20 and the variable resistor controls current flowthrough array 20 to a desired level. The present circuit may increaselighting system efficiency and reduce heat generated by the lightingsystem as compared to other approaches. In the example of FIG. 2, thevariable resistor 220 typically produces a voltage drop in the range of0.6V. However, the voltage drop at variable resistor 220 may be less orgreater than 0.6V depending on the variable resistor's design.

Thus, the circuit shown in FIG. 2 provides voltage feedback to a voltageregulator to control the voltage drop across array 20. For example,since operation of array 20 results in a voltage drop across array 20,voltage output by voltage regulator 204 is the desired voltage betweenarray 20 and variable resistor 220 plus the voltage drop across array220. If the resistance of variable resistor 220 is increased to decreasecurrent flow through array 20, the voltage regulator output is adjusted(e.g., decreased) to maintain the desired voltage between array 20 andvariable resistor 20. On the other hand, if the resistance of variableresistor 220 is decreased to increase current flow through array 20, thevoltage regulator output is adjusted (e.g., increased) to maintain thedesired voltage between array 20 and variable resistor 20. In this way,the voltage across array 20 and current through array 20 may besimultaneously adjusted to provide a desired light intensity output fromarray 20. In this example, current flow through array 20 is adjusted viaa device (e.g., variable resistor 220) located or positioned downstreamof array 20 (e.g., in the direction of current flow) and upstream of aground reference 260.

Referring now to FIG. 3, a schematic of a second lighting system circuitthat may be supplied varying amounts of current is shown. FIG. 3includes some of the same elements as the first lighting system circuitshown in FIG. 2. Elements in FIG. 3 that are the same as elements inFIG. 2 are labeled with the same numeric identifiers. For the sake ofbrevity, a description of same elements between FIG. 2 and FIG. 3 isomitted; however, the description of elements in FIG. 2 applies to theelements in FIG. 3 that have the same numerical identifiers.

The lighting system shown in FIG. 3 includes a SLM section 301 thatincludes array 20 which includes LEDs 110. The SLM also includes switch308 and current sense resistor 255. However, switch 308 and currentsense resistor may be included with voltage regulator 304 or as part ofcontroller 108 if desired. Voltage regulator 304 includes voltagedivider 310 which is comprised of resistor 313 and resistor 315.Conductor 340 puts voltage divider 310 into electrical communicationwith cathodes 202 of LEDs 110 and switch 308. Thus, the cathodes 202 ofLEDs 110, an input side 305 (e.g., a drain of a N channel MOSFET) ofswitch 308, and node 321 between resistors 313 and 315 are at a samevoltage potential. Switch 308 is operated in only open or closed states,and it does not operate as a variable resistor having a resistance thatcan be linearly or proportionately adjusted. Further, in one example,switch 308 has a Vds of 0 V as compared to 0.6V Vds for variableresistor 220 shown in FIG. 2.

The lighting system circuit of FIG. 3 also includes an error amplifier326 receiving a voltage that is indicative of current passing througharray 20 via conductor 340 as measured by current sense resistor 255.Error amplifier 326 also receives a reference voltage from controller108 or another device via conductor 319. Output from error amplifier 326is supplied to the input of pulse width modulator (PWM) 328. Output fromPWM is supplied to buck stage regulator 330, and buck stage regulator330 adjusts current supplied between a regulated DC power supply (e.g.,102 of FIG. 1) and array 20 from a position upstream of array 20.

In some examples, it may be desirable to adjust current to array via adevice located or upstream (e.g., in the direction of current flow) ofarray 20 instead of a position that is downstream of array 20 as isshown in FIG. 2. In the example lighting system of FIG. 3, a voltage thefeedback signal supplied via conductor 340 goes directly to voltageregulator 304. An intensity voltage control signal supplied viaconductor 319 from controller 108 becomes a reference signal Vref, andit is applied to error amplifier 326 rather than to the drive circuitfor a variable resistor.

The voltage regulator 304 directly controls the SLM current from aposition upstream of array 20. In particular, resistor divider network310 causes the buck regulator stage 330 to operate as a traditional buckregulator that monitors the output voltage of buck regulator stage 330when the SLM is disabled by opening switch 308. The SLM may selectivelyreceive an enable signal from conductor 302 which closes switch 308 andactivates the SLM to provide light. Buck regulator stage 330 operatesdifferently when a SLM enable signal is applied to conductor 302.Specifically, unlike more typical buck regulators, the buck regulatorcontrols the load current, the current to the SLM and how much currentis pushed through the SLM. In particular, when switch 308 is closed,current through array 20 is determined based on voltage that develops atnode 321.

The voltage at node 321 is based on the current flowing through currentsense resistor 255 and current flow in voltage divider 310. Thus, thevoltage at node 321 is representative of current flowing through array20. A voltage representing SLM current is compared to a referencevoltage that represents a desired current flow through the SLM. If theSLM current is different from the desired SLM current, an error voltagedevelops at the output of error amplifier 326. The error voltage adjustsa duty cycle of PWM generator 328 and a pulse train from PWM generator328 controls a charging time and a discharging time of a coil withinbuck stage 330. The coil charging and discharging timing adjusts anoutput voltage of voltage regulator 304. Since the resistance of array20 is constant, current flow through array 20 may be adjusted viaadjusting the voltage output from voltage regulator 304 and supplied toarray 20. If additional array current is desired, voltage output fromvoltage regulator 304 is increased. If reduced array current is desired,voltage output from voltage regulator 304 is decreased. FIG. 4 providesa more detailed description of the lighting system shown in FIG. 3.Those skilled in the art appreciate that the implementation of FIG. 3presents merely one possible circuit in accordance with the examplesdiscussed here.

Referring now to FIG. 4, a detailed view of the lighting systemdescribed in FIG. 3 is shown. The SLM portion 301 is at the left side ofthe diagram. The error amplifier 326 is at the bottom middle of thediagram, with the PWM generator 328 at the top of FIG. 4. The buckregulator stage 330 lies at the right side of FIG. 4. An enable signalGENABLE may be provided to the SLM at switch 308 via conductor 302. Inone example where switch 308 is a FET, the source of switch 308 is inelectrical communication with current sense resistor 255. A drain ofswitch 308 is in electrical communication with cathodes of array 20shown in FIG. 3.

Amplifier 473 applies a gain to the voltage at node 321 and outputs avoltage to amplifier 475 which represent current flow through array 20.Amplifier 475 compares current flow through array 20 and a desiredintensity SLM DRIVE which is indicative of a desired current flowthrough array 20. Amplifier 475 outputs a voltage at output 451 that isrepresentative of a difference between an intensity setting from SLMDRIVE (may be provided by controller 108 of FIG. 1) and the arraycurrent as is determined from voltage at node 321. Thus, the output oferror amplifier 326 is a voltage that represents a desired change incurrent, and where the desired change in current is based on adifference in current flowing through array 20 and a desired arraycurrent represented as an intensity level SLM DRIVE. The voltage outputfrom amplifier 326 is directed to PWM generator 328.

It should be noted that controlling current through array 20 to controllight intensity may provide more repeatable light intensity and improvedlighting device control as compared to controlling voltage across array.By controlling current through array 20 rather than voltage across array20, light intensity control may be improved because light intensityoutput from array 20 may change even though a constant voltage isapplied across array 20 because resistance or impedance of lightingsystem components may change with age, temperature, and other operatingconditions to affect current flow through array 20. Since lightintensity may be directly correlated to current flow through array 20,controlling current flow through array 20 may be a more effective way tocontrol light intensity of array 20 than controlling voltage acrossarray 20.

PWM generator section 328 includes a PNP transistor 404 that supplies aconstant current amount to capacitor 405. Timing circuit 401 operates topull capacitor 405 toward ground (GND) via an open collector transistor(not shown). Timing circuit 401 along with PNP transistor 404 andcapacitor 405 generate a ramping signal at a frequency that is relatedto the value of capacitor 403. In one example, timer circuit 401 is a555 timer. In one example, the timing circuit 401, capacitor 405, andPNP transistor 404 provide a 350 KHz ramping signal output to theinverting input of comparator 406. Comparator 406 receives its invertinginput (e.g.,—input) from timing circuit 401 including transistor 404 andcapacitor 405. Comparator 406 receives its non-inverting input from theoutput of error amplifier 326. The output 453 of comparator 406 goeshigh when a voltage at the inverting input is greater than the voltageat the non-inverting input. Comparator 406 outputs a pulse train with avarying duty cycle to buck stage 330. The pulse train duty cycle isrelated to an error between an actual current flow through array 20 anda desired current flow through array 20. The PWM generator section 328provides an output signal having a duty cycle corresponding to the levelof the error voltage that corresponds to a current flow error based oncurrent flow through array 20. If the DC level of the error voltage ismidlevel, the duty cycle is 50%. If the DC level goes up the duty cyclewill approach 100%.

Buck stage 330 includes a current driver 407 that supplies an increasedamount of current to switching devices 408 and 409 than may be sourcedby comparator 406. In one example, current driver 407 includes a boostconverter to increase the voltage supplied to the gate of switchingdevice 408 to a level 12 VDC above the voltage at the source ofswitching device 408 so that switching device 408 may be activated.Current driver 407 alternatively operates switching device 408 and 409to selectively charge and discharge inductor 426 via voltage supplied byDC voltage source 102. The output of inductor 426 is filtered viacapacitors 428, 430, and 432. The regulated voltage output from inductor426 is bucked down to lower than voltage output from DC voltage source102. Finally, the voltage output 455 from buck stage 330 is applied tothe anodes of LEDs in array 20 and to voltage divider 310.

In this way, current flow through array 20 is monitored and compared toa desired current flow through array 20. If the actual current flowthrough array 20 deviates from the desired current flow, output of thePWM generator is adjusted, thereby altering the charging and dischargingof inductor or coil 426. The voltage output from inductor or coil 426 isvaried in response to the difference in actual current flowing througharray 20 and desired current flow through array 20 to adjust voltageapplied to array 20 and current flow through array 20. Consequently, thevoltage output from buck stage 330 is adjusted responsive to a currentflow through array 20. It should be noted that array 20 represents aload applied to voltage regulator 304; however, the load may be any typeof electrical load.

Thus, the systems of FIGS. 1-4 provide for operating one or more lightemitting devices, comprising: a voltage regulator including a feedbackinput, the voltage regulator in electrical communication with the one ormore light emitting devices; and a current sensing device positioned ina current path through which a current passes through the one or morelight emitting devices. The system further comprises a currentcontrolling device positioned in the current path upstream of thecurrent sensing device and downstream of the one or more light emittingdevices. The system includes where the current controlling device is avariable resistor.

In some examples, the system includes where the variable resistor is aFET. The system also includes where the voltage regulator is a buckregulator. The system includes where the current sensing device indirect electrical communication with the feedback input. The system alsoincludes where the feedback input is in direct electrical communicationwith an electrical node positioned between the one or more lightemitting devices and a variable resistor, and where the variableresistor is positioned upstream of the current sensing device in thecurrent path. The system also includes where the feedback input is avoltage input receiving a voltage at a cathode of the one or more lightemitting devices.

In another example, the systems of FIGS. 1-4 provide for operating oneor more light emitting devices, comprising: a current controlled voltageregulator including a current feedback input, the current controlledvoltage regulator in electrical communication with the one or more lightemitting devices; and a current sensing device positioned in a currentpath through which a current passes through the one or more lightemitting devices, the current sensing device in direct electricalcommunication with the current feedback input. The system includes wherethe current controlled voltage regulator includes a lighting devicearray current error amplifier.

In some examples, the system includes where the current controlledvoltage regulator includes a pulse width modulated generator. The systemincludes where the current controlled voltage regulator includes a buckstage that receives a supply voltage from a DC voltage source. Thesystem includes where the lighting device array current error amplifieris electrically coupled to the pulse width modulation generator, andwhere an output of the pulse width modulation generator is input to thebuck stage. The system further comprises a controller, the controllerincluding instructions for adjusting a light intensity of the one ormore light emitting devices.

Referring now to FIG. 5, a method for operating the lighting systems asdescribed in FIGS. 1-4 is shown. The method of FIG. 5 may be stored innon-transitory memory of controller 108 shown in FIG. 1 as executableinstructions.

At 502, method 500 judges whether or not there has been a request toactivate a lighting system. In one example, the lighting system is asshown in FIGS. 1-4. A request to activate the lighting system may beinitiated via an operator command (e.g., activation of a switch) or viaa controller command. The request to activate the lighting system may beinput to a controller 108 shown in FIG. 1. If method 500 determines arequest to activate the lighting system is present, the answer is yesand method 500 proceeds to 504. Otherwise, the answer is no and method500 proceeds to exit.

At 504, method 500 determines a desired intensity (e.g., lumen output)for the lighting array. The desired intensity may be based on the typeof lighting device, curing parameters, work piece conditions, or otheroperating conditions. The desired intensity may correspond to a specificcurrent flow rate through the lighting array. For example, a lightingintensity of X lumens may be provided when Y amps flow through the arrayof lighting devices. In one example, the lighting intensity is used toindex a table or function of empirically determined values of electricalcurrent that provide the desired lighting intensity. Method 500 proceedsto 506 after the desired lighting intensity is determined.

At 506, method 500 judges whether or not a current controlled voltageregulator is present in the lighting system. In one example, method 500judges that a current controlled voltage regulator is in the lightingsystem when a particular bit is set in memory. If method 500 judges thata current controlled voltage regulator is in the present lightingsystem, the answer is yes and method 500 proceeds to 516. Otherwise, theanswer is no and method 500 proceeds to 508.

At 508, method 500 adjusts current flowing through an array of lightingdevices (e.g., array 20 of FIG. 1) to provide a desired lightingintensity. In one example, the desired lighting intensity is increasedvia increasing a voltage that represents a desired lighting intensityand current flow through the light array. Similarly, a desired lightingintensity may be reduced via decreasing the voltage that represents thedesired lighting intensity and current flow through the light array. Thevoltage is adjusted to a value that represents the desired lightingintensity as determined at 504. In one example, a controller outputs ananalog voltage that corresponds to the desired lighting intensity andcurrent flow through the lighting array.

The desired light intensity voltage is applied to a variable resistor toadjust current flow through the light array. Current flow through thelight array may be adjusted linearly or proportionately with the desiredlight intensity voltage. In one example, the desired light intensityvoltage is applied according to FIG. 2 via conductor 230 to a drivecircuit 222 and output from the drive circuit is applied to controlvariable resistor 220. Method 500 proceeds to 510 after the current flowthrough the lighting array is adjusted.

At 510, method 500 determines an amount of current flowing through thelighting array. In one example, a current sensing resistor (e.g.,resistor 255 shown in FIG. 2) is placed in a current path in whichcurrent from a lighting array flows. If current flows through thelighting array, a voltage develops across the sense resistor. Thevoltage may be directed to a controller (e.g., controller 108 of FIG. 1)that converts the voltage to a current based on ohm's law. Method 500proceeds to 512 after current flowing through the lighting array isdetermined.

At 512, method 500 adjusts electrical current flowing through thelighting array. In one example, the electrical current flowing throughthe lighting array is adjusted via changing a resistance value of avariable resistor placed in series with a lighting array and differentlevels of electrical potential (e.g., ground and V+). The resistance ofthe variable resistor may be adjusted by a controller or an amplifier.In one example, a controller converts current flow through the lightarray as determined at 510 to a light intensity via a transfer functionor empirically determined table of values. The controller also comparesthe light intensity to a desired light intensity. Alternatively,electrical current flow through the lighting array and desired currentflow through the lighting array may be used in place of light intensity.If the light intensity is different from the desired light intensity, acontrol signal applied to a driver is adjusted so that the resistancevalue of the variable resistor 220 is adjusted such that current flowthrough the lighting array converges to the desired current flow throughthe lighting array. For example, if desired lighting array current isgreater than actual lighting array current, the resistance value of thevariable resistor is decreased. Alternatively, if the desired lightingarray current is less than actual lighting array current, the resistancevalue of the variable resistor is increased. In this way, current flowthrough the lighting array is adjusted in a closed loop manner. Method500 proceeds to 514 after current flow through the lighting array isadjusted.

At 514, method 500 adjusts voltage output from a voltage regulator tomaintain a desired voltage at a location in a circuit that is downstreamof a lighting array according to a direction of current flow through thelighting array. In one example, a voltage at a location downstream of alighting array is input to a voltage feedback input of a voltageregulator. The voltage regulator adjusts output of the voltage regulatorto provide a desired voltage at the location downstream of the lightingarray. In particular, the voltage at the location downstream of thelighting array is compared to a desired voltage. If there is adifference between the two voltages, the output of the voltage regulatoris adjusted to provide the desired voltage. For example, if the voltagedownstream of the lighting array is less than desired, output voltage ofthe voltage regulator is increased until the voltage downstream of thelighting array matches the desired voltage. In this way, output of thevoltage regulator is adjusted so that a desired current flow through thelighting array may be provided by changing a value of the variableresistor. Method 500 proceeds to exit after the output voltage of thevoltage regulator is adjusted.

At 516, method 500 adjusts a voltage applied across a lighting array inresponse to a desired lighting intensity as determined at 504. In oneexample, the voltage output of a buck regulator (e.g., see FIG. 4) isadjusted in response to a voltage that represents a desired lightintensity. The voltage representing the desired light intensity orcurrent flow through the lighting array is input to a lighting arraycurrent error stage. Note that current flow through the lighting arraymay be correlated to a lighting intensity. The lighting array currenterror stage compares lighting array current to desired lighting arraycurrent or lighting intensity and a signal for adjusting buck voltageregulator output is provided to adjust buck regulator output. Method 500proceeds from 516 to 518 after voltage applied across the lighting arrayis adjusted.

At 518, method 500 determines an amount of current flowing through alighting array as described at 510. Specifically, current flow through alighting array is determined based on a voltage that develops across acurrent sense resistor (e.g., 255 of FIG. 3). Method 500 proceeds to 520after current flow through the lighting array is determined.

At 520, method 500 adjusts electrical current flow through the lightingarray via adjusting voltage applied across the lighting array. In thisexample, a voltage representing electrical current flowing through array20 is input to a lighting array current error stage (e.g., 326 of FIG.3) of a voltage regulator supplying power to a lighting array. Thevoltage representing current flow through the lighting array issubtracted from a desired current flowing through the lighting array ora lighting intensity to produce an error signal. The error signal isinput to a pulse width modulation generator to produce a pulse widthmodulated voltage output that is proportional to the lighting arraycurrent error. The pulse width modulated voltage output is input to abuck regulator and voltage output of the buck regulator is adjusted inresponse to the pulse width modulated voltage. Such operation isdescribed in FIGS. 3 and 4. In this way, the buck voltage regulator iscurrent controlled so as to cause current flow through the lightingarray to converge to the desired current and lighting intensity. Method500 proceeds to exit after current flowing through the lighting array isadjusted via increasing or decreasing voltage output from the buckvoltage regulator.

Thus, the method of FIG. 5 provides for a method for operating one ormore light emitting devices, comprising: supplying electrical power toone or more light emitting devices via a voltage regulator; andadjusting current flow through the one or more light emitting devices inresponse to a current flowing through the one or more light emittingdevices. The method includes where the current flowing through the oneor more light emitting devices is controlled via a variable resistancedevice. The method also includes where adjusting current flow throughthe one or more light emitting devices includes adjusting a voltageoutput from the voltage regulator in response to the current flowingthrough the one or more light emitting devices.

In another example, the method also includes where the current flowingthrough the one or more light emitting devices is controlled viaadjusting a voltage output from the voltage regulator. The methodfurther comprises adjusting the voltage output from the voltageregulator in response to a light array current error. The method furthercomprises adjusting the voltage output from the voltage regulator inresponse to output of a pulse width modulation generator.

As will be appreciated by one of ordinary skill in the art, the methodsdescribed in FIG. 5 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,lighting sources producing different wavelengths of light may takeadvantage of the present description.

The invention claimed is:
 1. A system for operating one or more lightemitting devices, comprising: a voltage regulator including a voltagefeedback input receiving input from a voltage divider networkelectrically coupled to cathodes of the one or more light emittingdevices, the voltage regulator in electrical communication with an inputof a current controlling device and cathodes of the one or more lightemitting devices, the voltage regulator including an error amplifier;and a current sensing device positioned in a current path through whicha current passes through the one or more light emitting devices, thecurrent sensing device in electrical communication with a controllerdifferent than the voltage regulator, the controller includinginstructions to adjust light intensity of the one or more light emittingdevices.
 2. The system of claim 1, where the controller instructionsadjust lighting intensity via the current controlling device and wherethe voltage regulator further comprises a pulse width generator and abuck stage amplifier.
 3. The system of claim 2, where the currentcontrolling device is a variable resistor.
 4. The system of claim 3,where the variable resistor is a FET.
 5. The system of claim 1, wherethe voltage regulator is a buck regulator.
 6. The system of claim 1,where the current sensing device is in electrical communication with thevoltage feedback input.
 7. The system of claim 1, where the voltagefeedback input is in direct electrical communication with an electricalnode positioned between the one or more light emitting devices and avariable resistor, and where the variable resistor is positionedupstream of the current sensing device in the current path.
 8. Thesystem of claim 1, where the voltage feedback input is a voltage inputreceiving a voltage at a cathode of the one or more light emittingdevices.
 9. A system for operating one or more light emitting devices,comprising: a current controlled voltage regulator including a currentfeedback input, the current controlled voltage regulator in electricalcommunication with the one or more light emitting devices, the currentcontrolled voltage regulator including an error amplifier that iselectrically coupled to a pulse width modulation generator, and where anoutput of the pulse width modulation generator is input to a buck stageamplifier; and a current sensing device positioned in a current paththrough which a current passes through the one or more light emittingdevices, the current sensing device in direct electrical communicationwith the current feedback input.
 10. The system of claim 9, furthercomprising a controller including controller instructions to supply areference signal to the error amplifier.
 11. The system of claim 9,where the error amplifier includes two amplifiers.
 12. The system ofclaim 11, where a first of the two amplifiers applies a gain to avoltage at cathodes of the one or more light emitting devices.
 13. Thesystem of claim 11, where a second of the two amplifiers is inelectrical communication with a comparator of the pulse width modulationgenerator.
 14. The system of claim 9, where the buck stage amplifierincludes two switches.